1. Field of the Invention
The present invention relates to a multichannel digital magnetic recording apparatus. More specifically, the present invention relates to a multichannel magnetic recording apparatus for writing digital signals on a magnetic recording medium in multichannels using thin film magnetic heads.
2. Description of the Prior Art
Since a thin film magnetic head includes a lesser number of turns as compared with a winding type magnetic head, a writing current as large as several amperes is required in writing data in a magnetic recording medium such as a magnetic tape, magnetic disk, magnetic drum or the like using the same. However, when such a large writing current flows into a thin film magnetic head, such a thin film magnetic head may suffer thermal damage. Therefore, conventionally the following approach was employed to prevent the above described thermal damage.
FIG. 1 is a graph showing a waveform of a current flowing through a winding of a thin film magnetic head of a conventional apparatus. An ordinary rectangular waveform recording current IR is converted into a recording current IP of a pulse train form to avoid thermal damage. A peak value of the recording current IR is Io and the minimum inversion interval is Tmin. The peak value of the recording current IP is likewise Io and the period of the pulse train is T and the pulse width of the pulse train is .DELTA.T. It is known that assuming that the gap length of the magnetic head is G.sub.l, the relative speed of the magnetic head and the recording medium is V and the period T of the pulse train is selected to satisfy the following formula, magnetization patterns on a recording medium when recorded by the recording current IR and when recorded by the recording current IP are equivalent to each other and the same outputs are obtained as the outputs from reproducing heads. ##EQU1##
Since the heat of the winding of the magnetic head is proportional to the square of a current flowing through the winding, assuming the period T=Tmin/2, for example, the heat amount of the winding decreases in proportion to (2.multidot..DELTA.T/T).sup.2 as the pulse width .DELTA.T is decreased with respect to the period T.
However, in the case where signals are written on a recording medium in multichannels by means of a plurality (N) of thin film magnetic heads, it is necessary that the current capacity of a power source for the apparatus is increased N times as compared with a case of a single channel. In addition, since thin film magnetic heads have a smaller number of turns and require an increased amount of current, it follows that a power supply capacity required by an apparatus becomes considerably large. Accordingly, it has been desired that an apparatus capable of reducing a power supply capacity is provided in the case of multichannels.